Julian Fellowes says in future Downton Abbey may have to be written without him. Below are a few pointers from his guide for designated scriptwriters...

1. Sport, religion and politics

According to my long-term outline, series 5 will begin in 1924 and end at Christmas 1925. This leaves room for Lady Mary to compete in the Winter Olympics at Chamonix, and for Lady Edith to cover the Scopes Monkey trial in Tennessee. Or they could have tea with Mussolini. It’s up to you.

2. In, out, shake it all about

There are so many characters in Downton that it’s sometimes difficult for them all to get a look-in. For this reason we operate a strict one-in, one-out policy, like a nightclub: if someone is born, someone must die.

3. The Maggie Smith factor

I never intended Downton to go to a second series, much less beyond. This has given rise to several logistical issues, the biggest of which is that the Dowager Duchess of Grantham will reach, by my reckoning, the age of 104 by the time Dame Maggie’s current contract expires. For consistency’s sake, keep her off the stairs.

4. Just say no to vampires

As time marches forward at Downton Abbey, so must the characters move with fashion, the plot must constantly be refreshed with revelations. But under no circumstances should any character ever be revealed to be a vampire. If it happens, you’re sacked.

5. Beware the modern age

Anachronisms will creep into the story from time to time — it’s an occupational hazard on this sort of series — so keep your guard up. Over the years I’ve caught dozens of errors at the first-reading stage — lines such as “If they can put a man on the moon, why can’t they make a spoon that fits into my egg?” — but it’s the one that sneaks through that the critics jump on. Beware!